Tunable coaxial line



1956 J. o. SILVEY ET AL 2,774,044

TUNAELE COAXIAL LINE.

"Filed Aug. 9, 1952 IN! 'ENTORS. JOHN o. SILVEY BY air/5 0. 500/909ATTORNEY United States Patent TUNABLE COAXIAL LINE John 0. Silvey, FortWayne, and Ortis C. Booher, Huntington, Ind., assignors to InternationalTelephone and Telegraph Corporation, a corporation of MarylandApplication August 9, 1952, Serial No. 303,456

2 Claims. (Cl. 33382) This invention relates to means for varying theelectrical length of a line, and particularly to means for varying theinductance of a line without varying the physical length thereof.

This invention has particular applicability to tuning circuits of thecoaxial line resonator type. Tunable coaxial resonator lines are knownwhich employ capacitive tuning for varying the frequency of the line. Anexample of such tuning is disclosed in the copending application SerialNo. 303,457, filed August 9, 1952, John O. Silvey inventor, assigned tothe same assignee as this application, wherein there is shown a tunerfor ultra high frequencies. Tuning or frequency variation isaccomplished by varying the capacity between the inner and outerconductors of the coaxial line resonator. The coaxial line isshort-circuited at one end and the capacity of the line is varied bypositioning at the open end of the line a cap surrounding a portion ofthe inner conductor and contacting the outer conductor, therebycontrolling the capacity between the conductors.

An important application of the present invention is in improving thetuning range of the above-mentioned coaxial line resonator by increasingthe electrical length of the line.

An important object of the present invention is the provision of asimple and economical means for varying the electrical length of thetuned line.

A feature of the invention is the provision of means for varying theelectrical length of the line without changing the physical lengththereof.

Another object of the present invention is to provide an improvedtunable circuit of the coaxial line type.

Another feature of the present invention is to provide an innerconductor for the coaxial line which is readily interchangeable andrequires no change in the coaxial line for the utilization thereof.

In accordance with one aspect of applicants invention there is provideda variable inductance line comprising a conductor having grooves formedon its surface thereof. A sleeve is provided which fits snugly over theconductor .and movably over the grooves to short circuit variablenumbers of said grooves, whereby the electrical length may be variedwithout changing the physical length of the line.

In accordance with another aspect of applicants invention, there isprovided a tunable coaxial line comprising an outer conductor and aninner conductor concentric therewith and spaced therefrom. The coaxialline is shorted at one end thereof and has positioned at the oppositeend a capacitive cap for varying the capacity between the conductors.The inner conductor has grooves formed over a portion thereof toincrease the inductance of the line so that the electrical length of theline is increased without increasing the physical length of the line.

The above-mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be ice best understood, by reference to the followingdescription of an embodiment of the invention taken in conjunction withthe accompanying drawing, wherein the single figure shows across-sectional view of the tunable coaxial line resonator forming anembodiment of this invention.

Referring to the figure, there is shown a tunable coaxial line resonatorcomprising an outer conductor 1 and an inner conductor 2 concentrictherewith and spaced therefrom. One end of the coaxial line may beshorted as shown at 3. At the open end of the line there is shown amovable conductive cap which is positioned over a portion of the innerconductor 2 and makes contact with outer conductor 1 by means, such aswiper strips 5. The conductive cap, which may be considered a capacitivecap since it varies the capacitance between the inner and outerconductors, has a threaded portion 6 which cooperates with a stationarythreaded member 7, so that by rotating the cap, it is made to movelongitudinally over the inner conductor 2.

The inner conductor has grooves generally indicated at 8 formed over aportion thereof to increase the inductance of the line. A sleeve 9having a flange 10 at one end thereof may be slidably mounted on theinner conductor 2. The electrical length, or the inductance of the lineis varied by moving the sleeve over the inner conductor 2, therebyshorting out a given number of grooves. At the shorted end 3 of thecoaxial line there is provided an opening 11 for accommodating anadjusting screw 12. The flange is provided with a tapped hole forengaging the screw 12 and controlling the movement sleeve 9.

Thus it is seen that tuning of the line is characterized by bothcapacitive and inductive adjustments; the capacitive adjustment by cap 4and the inductive adjustment by sleeve 9. By virtue of the capacitiveand inductive adjustment means, a somewhat greater frequency coverage ismade possible.

While we have described above the principles of our invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationof the scope of our invention as set forth in the objects thereof and inthe accompanying claims.

We claim:

1. A tunable coaxial line comprising, an outer conductor, an innerconductor concentric therewith and spaced therefrom, means forshort-circuiting said line at one end thereof, a movable conductive cappositioned at the opposite end of said line over a portion of said innerconductor and contacting said outer conductor, whereby the capacitybetween said conductors may be varied by moving said cap over said innerconductor; said inner conductor having circumferential grooves formedover a portion thereof, to increase the inductance of said line, asleeve fitting snugly over a given portion of said grooves and moveableto short circuit a variable number of said grooves, whereby theelectrical length of said line may be varied without increasing thephysical length of said line.

2. A tunable coaxial line comprising an outer conductor, an innerconductor concentric therewith and spaced therefrom, means forshcrt-circuiting said line at one end thereof, a movable conductive cappositioned at the opposite end of said line over a portion of said innerconductor and contacting said outer conductor, whereby the capacitybetween said conductors may be varied by moving said cap over said innerconductor; said inner conductor having circumferential grooves formedover a portion thereof, to increase the inductance of said line, asleeve fitting snugly over a given portion of said grooves and movableto short circuit a variable number of said line, whereby said threadedmember may be adjusted externally of said line to move the sleevelongitudinally along said inner conductor.

References Cited in the file of this patent UNITED STATES PATENTS DowApr. 18, Hahn Nov. 26, Guarrera Oct. 28, White Sept 11, Wolfe Oct. 23,Gurewitsch Dec. 18, Carlson June 9, Cutler NOV. 17, Pan Aug. 17, Pan eta1. July 26,

